Measuring torsion or bending of a part of the human or animal body, for example a knee or a neck may be of importance for science or therapy. Information obtained by such a measurement can be used to improve human or animal performance, for example in sports, and it may be used to prevent injuries caused by straining.
A body motion sensor is described in an article by Ravindra Wijesiriwardana, titled “Inductice Fiber-Meshed Strain and Displacement Transducers for Respiratory Measuring Systems and Motion Capturing Systems”, published in the IEEE sensors journal Vol 6, No 3 (kune 2006) pages 571-579. (EPO reference XP-002580465). This article proposes the use of electroconductive coils integrated into garments as transducers for measuring human limb motion. The coils are made by knitting conductive fibres into the fabric of garments. A coil with windings around the arm is described, with windings below the elbow, windings at the elbow and windings above the elbow. Measurement of the self inductance of a single coil comprising all windings or mutual inductance between coils with parts of the windings were used to measure bending of the elbow.
This makes it possible to measure the angle of the bend between two points above and below the elbow joint, when joint angle is approximated from measuring above and below the joint, the fulcrum or axis of rotation is assumed to be consistent between subjects, by monitoring the bend over the whole joint, differences or changes in the fulcrum or axis of rotation are included in the measurement. However, with this coil configuration it is difficult to measure whole bending. The mutual inductance sensor cannot measure the degree of rotation which can be a very important element in biomechanics of joints for example. The article is silent about the use of additional sensors.
EP 2 057 944 discloses a knee brace with a combination of an acceleration sensor and a optical fibre that is used as a device (goniometer) for measuring bending angle.
International patent application WO 2009/061181 discloses a method, a brace and a system for measuring an angle between a first and a second member, which elements may be pivoting limbs of humans or animals, like knee joints. With this known method an angle measuring sensor suitable for use under dynamic situations, is calibrated in a static situation by means of accelerometers. Said patent application discloses the use of an optical goniometer as an angle measuring sensor. More in particular it discloses the use of optical fibres or optical flexible tubes for measuring an angle.
A problem in using optical fibres for measuring an angle is that the degree of bending is limited to maximum angles of about 30 degrees due to possible cracking at larger angles and due to the fact that the light transmittance is only possible at relatively small angles. Further are such optical fibres fragile and prone to mechanical damage for instance of the so-called cladding layer, resulting in less accuracy and reduced performance, in particular reliability.
A network of body sensors is disclosed in an article by Kwang Yong Lim et al. titled “A Wearable, Self Calibrating. Wireless Sensor Network for Body Motion Processing”, published in the proceedings of the 2008 IEEE International Conference on Robotics and Automation, Pasadena, Calif., USA, May 19-23, 2008, pages 1017-1022 (EPO reference XP00258040464). Transmitters are used to transmit data from a plurality of motion sensors by wireless signal to a central processor. The article mentions a range of possible sensors, including accelerometers, a 3-axis magnetic sensor, gyroscopes and a linear encoder. More generally the article mentions that mechanical, inertial, acoustic, magnetic and optical sensing can be used, as well as fibre mesh sensing optical fibre loss, piezo-electric fabrics. The article describes a method of mathematical modelling of the output information from such sensors and fusion of the information from different sensors. Only the construction of the linear encoder is described in some detail.